/* Copyright 2017 Wolfgang Thaller. This file is part of Retro68. Retro68 is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. Retro68 is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with Retro68. If not, see <http://www.gnu.org/licenses/>.*/ #include "Section.h" #include "Symbol.h"#include "Reloc.h"#include "Object.h"#include "Symtab.h" #include <algorithm>#include <sstream>#include <assert.h>#include <iostream> #include "BinaryIO.h" using std::string; Section::~Section(){} Section::Section(Object& theObject, string name, int idx, SectionKind kind, Elf_Scn *elfsec) : theObject(theObject), name(name), idx(idx), kind(kind), elfsec(elfsec), relasec(NULL), exceptionInfoStart(0), codeID(-1), firstJTEntryIndex(0){ data = elf_getdata(elfsec, NULL); gelf_getshdr(elfsec, &shdr); outputBase = shdr.sh_addr;} void Section::SetRela(Elf_Scn *scn){ relasec = scn; GElf_Shdr rshdr; gelf_getshdr(relasec, &rshdr); int nRela = rshdr.sh_size / rshdr.sh_entsize; Elf_Data *data = elf_getdata(relasec, NULL); for(int i = 0; i < nRela; i++) { GElf_Rela rela; gelf_getrela(data, i, &rela); if(rela.r_offset < shdr.sh_addr || rela.r_offset > shdr.sh_addr + shdr.sh_size - 4) { // FIXME: There are sometimes relocations beyond the end of the sections // in LD output for some reason. That's bad. Let's ignore it. continue; } relocs.push_back(rela); } std::sort(relocs.begin(), relocs.end(), [](GElf_Rela& a, GElf_Rela& b) { return a.r_offset < b.r_offset; });} uint32_t Section::GetSize(){ return data->d_size;} string Section::GetData(){ return string((char*)data->d_buf, (char*)data->d_buf + data->d_size);} std::vector<RuntimeReloc> Section::GetRelocations(bool useOffsets){ std::vector<RuntimeReloc> outRelocs; for(auto& rela : relocs) { //printf("rel: %d %d %x %x\n", (int)GELF_R_TYPE(rela.r_info), (int)GELF_R_SYM(rela.r_info), (unsigned)rela.r_addend, (unsigned)rela.r_offset); int symidx = GELF_R_SYM(rela.r_info); if(symidx == 0) continue; Symbol& sym = theObject.symtab->GetSym(symidx); if(sym.st_shndx == SHN_UNDEF || sym.st_shndx >= SHN_LORESERVE) continue; if(sym.sectionKind == SectionKind::undefined) continue; uint32_t offset = rela.r_offset; if(useOffsets) offset -= shdr.sh_addr; if(GELF_R_TYPE(rela.r_info) == R_68K_32) { outRelocs.emplace_back(rela.relocBase, offset); } if(GELF_R_TYPE(rela.r_info) == R_68K_PC32 && sym.st_shndx != idx) { outRelocs.emplace_back(rela.relocBase, offset, true); } } return outRelocs;} void Section::ScanRelocs(){ for(Reloc& rela : relocs) { int symidx = GELF_R_SYM(rela.r_info); if(symidx == 0) continue; Symbol *sym = &theObject.symtab->GetSym(symidx); if(sym->st_shndx == SHN_UNDEF) continue; if(rela.r_addend != 0) { int symidx2 = theObject.symtab->FindSym(sym->st_shndx, sym->st_value + rela.r_addend); if(symidx2 != -1) { sym = &theObject.symtab->GetSym(symidx2); rela.r_addend = 0; rela.r_info = GELF_R_INFO(symidx2, GELF_R_TYPE(rela.r_info)); } } if(sym->st_shndx != idx) sym->referencedExternally = true; }} void Section::FixRelocs(bool allowDirectCodeRefs){ for(Reloc& rela : relocs) { if(GELF_R_TYPE(rela.r_info) != R_68K_32 && GELF_R_TYPE(rela.r_info) != R_68K_PC32) continue; int symidx = GELF_R_SYM(rela.r_info); if(symidx == 0) continue; Symbol& sym = theObject.symtab->GetSym(symidx); if(sym.sectionKind == SectionKind::undefined) continue; if(GELF_R_TYPE(rela.r_info) == R_68K_PC32 && sym.st_shndx == idx) continue; RelocBase relocBase; switch(sym.sectionKind) { case SectionKind::code: relocBase = RelocBase::code; if(exceptionInfoStart != 0 && rela.r_offset >= exceptionInfoStart && sym.name != "__gxx_personality_v0") { // Case 1: // references from .eh_frame, with the exception of __gcc_personality_v0. // Should be direct references within the code segment. if(sym.section.get() != this) {#if 0 std::cerr << "Warning: clearing cross-segment reference from .eh_frame:\n" << sym.name << " (" << name << "->" << sym.section->name << ")\n"; std::cerr << std::hex << (int)sym.st_info << " " << (int)sym.st_other << std::endl; //assert(GELF_ST_BIND(sym.st_info) == STB_WEAK);#endif /* ld behaves differently depending on whether debug info is present. If debug info is present, .eh_frame sections will contain references to other code segments, if no debug info is generated (or it is stripped at link time), then these pointers are set to 0 during linking. In most cases, this has to do with weak symbols; the instance of the symbol that is removed gets a null ptr (with R_68K_NONE relocation) in the .eh_frame section if there is no debug info, but gets remapped to the surviving instance if there is debug info. It also happens with some section symbols, and I *hope* this is related. This makes no sense to me, but the reason is probably buried somewhere within a 900-line function of C code within a 15000 line source file in GNU bfd. I *hope* that the correct behavior is to just clear those pointers. */ uint8_t *relocand = ((uint8_t*) data->d_buf + rela.r_offset - shdr.sh_addr); relocand[0] = relocand[1] = relocand[2] = relocand[3] = 0; rela.r_info = 0; } } else if(sym.needsJT) { // Case 2: References to code that can go through the jump table. // If we need an addend, that's a problem and we abort. if(rela.r_addend == 0) { relocBase = RelocBase::jumptable; } else { if(sym.section.get() != this) { std::cerr << "Invalid ref from " << name << ":" << std::hex << rela.r_offset-shdr.sh_addr << std::dec << " to " << sym.section->name << "(" << sym.name << ")" << "+" << rela.r_offset << std::endl; } assert(sym.section.get() == this); } } else if(allowDirectCodeRefs) { // Case 3: Direct Code Refs are allowed (single-segment exectuable), // We are happy. Nothing to check or do. } else { // Case 4: Multi-segment executable. // Code references that don't go through the jump table // must remain in the current segment. if(sym.section.get() != this) { // Should never happen because symbols that are referenced from a different // segment get their needsJT flag set (ScanRelocs and Obejct::MultiSegmentApp). std::cerr << "Invalid ref from " << name << ":" << std::hex << rela.r_offset-shdr.sh_addr << std::dec << " to " << sym.section->name << "(" << sym.name << ")" << "+" << rela.r_offset << std::endl; std::cerr << "needsJT: " << (sym.needsJT ? "true" : "false") << std::endl; std::cerr << "from addr: " << rela.r_offset << ", exceptionInfoStart: " << exceptionInfoStart << std::endl; } assert(sym.section.get() == this); } break; case SectionKind::data: relocBase = RelocBase::data; break; case SectionKind::bss: relocBase = RelocBase::bss; break; case SectionKind::undefined: assert(false); break; } if(!GELF_R_SYM(rela.r_info)) continue; // symboil reference has been cleared in Case 1 above rela.relocBase = relocBase; uint8_t *relocand = ((uint8_t*) data->d_buf + rela.r_offset - shdr.sh_addr); if(relocBase == RelocBase::jumptable) { uint32_t dst = 0x20 + sym.jtIndex * 8 + 2; relocand[0] = dst >> 24; relocand[1] = dst >> 16; relocand[2] = dst >> 8; relocand[3] = dst; } else { uint32_t orig = (relocand[0] << 24) | (relocand[1] << 16) | (relocand[2] << 8) | relocand[3]; uint32_t dst = orig + sym.section->outputBase - sym.section->shdr.sh_addr; relocand[0] = dst >> 24; relocand[1] = dst >> 16; relocand[2] = dst >> 8; relocand[3] = dst; } }}
/*
Copyright 2017 Wolfgang Thaller.
This file is part of Retro68.
Retro68 is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Retro68 is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with Retro68. If not, see <http://www.gnu.org/licenses/>.
*/
#include "Section.h"
#include "Symbol.h"
#include "Reloc.h"
#include "Object.h"
#include "Symtab.h"
#include <algorithm>
#include <sstream>
#include <assert.h>
#include <iostream>
#include "BinaryIO.h"
using std::string;
Section::~Section()
{
}
Section::Section(Object& theObject, string name, int idx, SectionKind kind, Elf_Scn *elfsec)
: theObject(theObject),
name(name), idx(idx), kind(kind), elfsec(elfsec), relasec(NULL),
exceptionInfoStart(0),
codeID(-1), firstJTEntryIndex(0)
{
data = elf_getdata(elfsec, NULL);
gelf_getshdr(elfsec, &shdr);
outputBase = shdr.sh_addr;
}
void Section::SetRela(Elf_Scn *scn)
{
relasec = scn;
GElf_Shdr rshdr;
gelf_getshdr(relasec, &rshdr);
int nRela = rshdr.sh_size / rshdr.sh_entsize;
Elf_Data *data = elf_getdata(relasec, NULL);
for(int i = 0; i < nRela; i++)
{
GElf_Rela rela;
gelf_getrela(data, i, &rela);
if(rela.r_offset < shdr.sh_addr || rela.r_offset > shdr.sh_addr + shdr.sh_size - 4)
{
// FIXME: There are sometimes relocations beyond the end of the sections
// in LD output for some reason. That's bad. Let's ignore it.
continue;
}
relocs.push_back(rela);
}
std::sort(relocs.begin(), relocs.end(),
[](GElf_Rela& a, GElf_Rela& b) { return a.r_offset < b.r_offset; });
}
uint32_t Section::GetSize()
{
return data->d_size;
}
string Section::GetData()
{
return string((char*)data->d_buf, (char*)data->d_buf + data->d_size);
}
std::vector<RuntimeReloc> Section::GetRelocations(bool useOffsets)
{
std::vector<RuntimeReloc> outRelocs;
for(auto& rela : relocs)
{
//printf("rel: %d %d %x %x\n", (int)GELF_R_TYPE(rela.r_info), (int)GELF_R_SYM(rela.r_info), (unsigned)rela.r_addend, (unsigned)rela.r_offset);
int symidx = GELF_R_SYM(rela.r_info);
if(symidx == 0)
continue;
Symbol& sym = theObject.symtab->GetSym(symidx);
if(sym.st_shndx == SHN_UNDEF || sym.st_shndx >= SHN_LORESERVE)
continue;
if(sym.sectionKind == SectionKind::undefined)
continue;
uint32_t offset = rela.r_offset;
if(useOffsets)
offset -= shdr.sh_addr;
if(GELF_R_TYPE(rela.r_info) == R_68K_32)
{
outRelocs.emplace_back(rela.relocBase, offset);
}
if(GELF_R_TYPE(rela.r_info) == R_68K_PC32
&& sym.st_shndx != idx)
{
outRelocs.emplace_back(rela.relocBase, offset, true);
}
}
return outRelocs;
}
void Section::ScanRelocs()
{
for(Reloc& rela : relocs)
{
int symidx = GELF_R_SYM(rela.r_info);
if(symidx == 0)
continue;
Symbol *sym = &theObject.symtab->GetSym(symidx);
if(sym->st_shndx == SHN_UNDEF)
continue;
if(rela.r_addend != 0)
{
int symidx2 = theObject.symtab->FindSym(sym->st_shndx, sym->st_value + rela.r_addend);
if(symidx2 != -1)
{
sym = &theObject.symtab->GetSym(symidx2);
rela.r_addend = 0;
rela.r_info = GELF_R_INFO(symidx2, GELF_R_TYPE(rela.r_info));
}
}
if(sym->st_shndx != idx)
sym->referencedExternally = true;
}
}
void Section::FixRelocs(bool allowDirectCodeRefs)
{
for(Reloc& rela : relocs)
{
if(GELF_R_TYPE(rela.r_info) != R_68K_32 && GELF_R_TYPE(rela.r_info) != R_68K_PC32)
continue;
int symidx = GELF_R_SYM(rela.r_info);
if(symidx == 0)
continue;
Symbol& sym = theObject.symtab->GetSym(symidx);
if(sym.sectionKind == SectionKind::undefined)
continue;
if(GELF_R_TYPE(rela.r_info) == R_68K_PC32 && sym.st_shndx == idx)
continue;
RelocBase relocBase;
switch(sym.sectionKind)
{
case SectionKind::code:
relocBase = RelocBase::code;
if(exceptionInfoStart != 0 && rela.r_offset >= exceptionInfoStart
&& sym.name != "__gxx_personality_v0")
{
// Case 1:
// references from .eh_frame, with the exception of __gcc_personality_v0.
// Should be direct references within the code segment.
if(sym.section.get() != this)
{
#if 0
std::cerr << "Warning: clearing cross-segment reference from .eh_frame:\n"
<< sym.name << " (" << name << "->" << sym.section->name << ")\n";
std::cerr << std::hex << (int)sym.st_info << " " << (int)sym.st_other << std::endl;
//assert(GELF_ST_BIND(sym.st_info) == STB_WEAK);
#endif
/*
ld behaves differently depending on whether debug info is present.
If debug info is present, .eh_frame sections will contain references
to other code segments, if no debug info is generated (or it is
stripped at link time), then these pointers are set to 0 during linking.
In most cases, this has to do with weak symbols; the instance of the
symbol that is removed gets a null ptr (with R_68K_NONE relocation) in
the .eh_frame section if there is no debug info, but gets remapped to
the surviving instance if there is debug info.
It also happens with some section symbols, and I *hope* this is related.
This makes no sense to me, but the reason is probably buried somewhere
within a 900-line function of C code within a 15000 line source file
in GNU bfd.
I *hope* that the correct behavior is to just clear those pointers.
*/
uint8_t *relocand = ((uint8_t*) data->d_buf + rela.r_offset - shdr.sh_addr);
relocand[0] = relocand[1] = relocand[2] = relocand[3] = 0;
rela.r_info = 0;
}
}
else if(sym.needsJT)
{
// Case 2: References to code that can go through the jump table.
// If we need an addend, that's a problem and we abort.
if(rela.r_addend == 0)
{
relocBase = RelocBase::jumptable;
}
else
{
if(sym.section.get() != this)
{
std::cerr << "Invalid ref from "
<< name << ":" << std::hex << rela.r_offset-shdr.sh_addr << std::dec
<< " to " << sym.section->name
<< "(" << sym.name << ")"
<< "+" << rela.r_offset << std::endl;
}
assert(sym.section.get() == this);
}
}
else if(allowDirectCodeRefs)
{
// Case 3: Direct Code Refs are allowed (single-segment exectuable),
// We are happy. Nothing to check or do.
}
else
{
// Case 4: Multi-segment executable.
// Code references that don't go through the jump table
// must remain in the current segment.
if(sym.section.get() != this)
{
// Should never happen because symbols that are referenced from a different
// segment get their needsJT flag set (ScanRelocs and Obejct::MultiSegmentApp).
std::cerr << "Invalid ref from "
<< name << ":" << std::hex << rela.r_offset-shdr.sh_addr << std::dec
<< " to " << sym.section->name
<< "(" << sym.name << ")"
<< "+" << rela.r_offset << std::endl;
std::cerr << "needsJT: " << (sym.needsJT ? "true" : "false") << std::endl;
std::cerr << "from addr: " << rela.r_offset << ", exceptionInfoStart: " << exceptionInfoStart << std::endl;
}
assert(sym.section.get() == this);
}
break;
case SectionKind::data:
relocBase = RelocBase::data;
break;
case SectionKind::bss:
relocBase = RelocBase::bss;
break;
case SectionKind::undefined:
assert(false);
break;
}
if(!GELF_R_SYM(rela.r_info))
continue; // symboil reference has been cleared in Case 1 above
rela.relocBase = relocBase;
uint8_t *relocand = ((uint8_t*) data->d_buf + rela.r_offset - shdr.sh_addr);
if(relocBase == RelocBase::jumptable)
{
uint32_t dst = 0x20 + sym.jtIndex * 8 + 2;
relocand[0] = dst >> 24;
relocand[1] = dst >> 16;
relocand[2] = dst >> 8;
relocand[3] = dst;
}
else
{
uint32_t orig = (relocand[0] << 24) | (relocand[1] << 16) | (relocand[2] << 8) | relocand[3];
uint32_t dst = orig + sym.section->outputBase - sym.section->shdr.sh_addr;
relocand[0] = dst >> 24;
relocand[1] = dst >> 16;
relocand[2] = dst >> 8;
relocand[3] = dst;
}
}
}